Spray guns having a fixed electrostatic head



M. A. R. POINT April 23, 1963 A SPRAY GUNS HAVING A FIXED ELETROSTATICHEAD Filed April 25. leso .E E x Inventor April 23, i963 y M. A. R.PoxNT SPRAY GUNS HAVING A FIXED ELECTROSTATIC HEAD Filed April 25.. 19602 Sheets-Sheet 2 @ad venlvor4 '415744' VS2""A ttameyg iinite ttes3,986,711 SPRAY GUNS HAVING A FIXED ELECTRO- STATIC HEAD Marcel AugustRoger Point, Grenoble, France, assigner to Societe Anonyme de MachinesElecrostatiques, Grenoble, France, a French body corporate Filed Apr.25, 1960, Ser. No. 24,582 Claims priority, application France Apr. 27,1959 11 Claims. (Cl. 239-15) Electrostatic spray guns are known having arotating head yfor atomizing and spraying tine particles, such as paint,on to an object to be coated.

In certain cases and for certain applications it may be advantageous tohave a gun having a iixed, i.e. non-rotatable, electrostatic head.

The present invention consists in a spray gun having a xed electrostatichead for atomizing and spraying tine particles of a materiahfor examplepaint, wherein said Afixed head comprises a zone provided with severalsmall atomizing orifices through which passes the material to be sprayedand a movable rotating member is in contact with the internal surface ofthis zone to act as a scraper ensuring a substantially uniformdistribution on said internal-surface of the material to be sprayed andpreventing the orifices from becoming obstructed or clogged.

In order that the invention may be more fully understood, someembodiments thereof will now be described with reference to theaccompanying drawings, in which:

FIGURE 1 lis an axial longitudinal section of a first embodimentaccording to the present invention;

FIGURE 2 is a partial lsection on a 4larger scale of the electrostatichead of FIGURE 1.

FIGURE 3 is an axial longitudinal section of a second embodiment of theinvention.

FIGURE 4 is an end view of the head in FIGURE 3.

FIGURE 5 shows how it is possible to regulate the delivery of theproduct to be atomized, and

FIGURE 6 is an axial longitudinal section of a third embodimentaccording to the invention.

FIGURE l shows a gun for electrostatic atom-izing and sprayingcomprising a metallic hand grip or butt 1 to which is fixed in anyappropriate manner an elongated insulating body 2 having a generallycylindrical shape. Through the butt extends a duct 3 for the feeding ofthe product under pressure to be atomized; an electric low tension cable4 for feeding a motor 5 whose function will be explained later on; and ahigh tension cable 6 intended to feed this high tension to theelectorstatic head for atomizing and spraying of tine particles of paintor other material. The butt 1 also carries a trigger 7 which may beoperated by the user. By means of this trigger it is possible to controlas desired through the intermediary of a pivoted rod 8, a switch 9 ofany suitable type in order to start or stop the electric motor 5. Thetrigger 7 also has a further function which will be described below.

The electrostatic head 16 of FIGURE 1 is shown in part-section on alarger scale in FIGURE 2. This head is cylindrical and has thin walls.It is provided towards its end with spraying holes 11, arranged forexample in several circular rows and radially directed towards theexterior. These holes have a diameter which may range from one toseveral tenths of a millimeter and serve for the discharge of theproduct to be atomized, the latter arriving through the duct 3 from anysuitable external source, under a pressure of a few atmospheres forexample from 2 to 3 kga/cm?.

In the absence of an electric field, the fine jets of product would bedirected radially towards the exterior along the axis of the holes.However, in the presence of an electric field caused by the highten-sion applied through the cable 6, the action of the electrostaticforces causes these jets of product to divide rise to line particlescharged with electricity which the electric ield directs thereafter onthe objects to be coated.

In order to avoid the holes 11 becoming obstructed, an internal rotatingscraper 12 is provided, which is driven by the motor 5 through aninsulating shaft 13. This scraper acts in the manner of anelectric'razor, its edges bearing against the internal surface of thehead 10 in the zone of the holes 11.

In order to regulate the delivery from the head '10, an external sleeve14 is provided whose internal surface may slide longitudinally withfriction on the external surface of the head 10, in order to obturate alarger or smaller number of holes 11. Thus, in FIGURE 2 the sleeve 143occupies a position such that only a single row of holes 11 mayfunction. In the example shown the sleeve 14 could also obstruct oruncover the two rows of holes 11, according to the wish of the user.

The corresponding longitudinal displacements of the sleeve arecontrolled by the trigger 7, which is mechanically connected to saidsleeve by an insulating rod 15, which enables the user to control thedelivery from the head 10. It is obvious that the adjustment of thelongitudinal position of the sleeve does not normal-ly cause the switch9 to `be operated unless the trigger 7 returns to its rest position asthe wish of the user.

Obviously the invention is in no way limited to the number andarrangement of holes shown in FIGURE 2.

It is moreover possible to provide a high tension electrode 16 of metalor high resistivity material in order to avoid the dispersion of theelectric eld and direct its lines of force towards the object to ybecoated. Thus the directional action of the eld is reinforced and at thesame time the protection of the operator is improved.

Lastly, an electric protection resistor may be provided, which is notshown, and be inserted between the end of the high tension cable 6 andthe head 10.

FIGURE 3 shows a longitudinal section of a second embodiment accordingto theV invention. Elements corresponding to those in FIGURE l have thesame reference numbers.

The butt 1 and insulating elongated body 2 are again shown. The hightension cable 6 passes through the butt, as well as the supply duct 3for the product to be atomized. A trigger 7 enables the operation to beadjusted (as will be described hereunder in more detail) by acting on ahinged rod 8.

In this embodiment the holes 11, as may be clearly seen on FIGURE 4, aredisposed on the plane end wall of the head 10 and are arranged in acircle and with suitable spacing from each other.

In order to ensure the rotation of theY internal rotating scraper 12,the arrival under pressure of the product through the duct 3 isutilised, in order to actuate a turbine rotor 1S. This rotor is ofhelical form and is in electric communication with the high tensioncable 6, through an electric protection resistor 17. "Preferably, adamping course be zero.

spring 19 is inserted between the rotor 18 and the scraper 12.

The product under pressure thus rotates the scraper 12 and the excess ofproduct not used for atomizing returns to a tank, not shown, through aduct 20 communicating with the head and passing through the butt 1 ofthe gun. (FIGURE 3).

In order to adjust the delivery from the head, two valves 21 and 22 havebeen arranged in the inlet duct 3 and return duct which may beconstructed for example in the form of a two-way cock, controlled by therod 8 pivoted to the trigger 7. The inlet duct 3 is obtained when thereturn duct 20 is open and vice versa.

By referring to FIGURE 5, it can be seen that the delivery is at amaximum when the duct 3 is open and when the duct 20 is closed. In thiscase, all the product arriving through the duct 3 is used for atomizing.If the duct 3 is closed and the duct 20 is open the delivery will of Inan intermediate position of the rod 8 (and of the trigger 7) thedelivery may be adjusted between its maximum and zero values.

Finally, FIGURE 6 shows in section a third embodiment of the invention.

In this embodiment, the scraper is also driven by means of the rotor 18,rotated by the stream of the product to be atomized and the vholes 11 ofthe head are disposed as in the embodiment of FIGURE 4.

-Also in this third embodiment the high tension cable 6 is connected tothe head 10 through an electric protection resistor 17. Moreover, therotor 18 as well as its housing are made 'of an insulating material.Thus the only metallic elements are the grill or end wall of the head10, and possibly the scraper 12.

In order to enhance the charge of the particles of paint or otherproduct, it is possible to provide the high tension grill with points orspikes standing on end, not shown, or to provide a disc having a thindischarge edge. This would moreover produce an automatic lowering of thehigh tension if the operator brings the gun too near to the object to becoated. The spark which might possibly arise under these conditionswould be produced at a lower voltage since the energy expended in thisspark is proportional to the square of said voltage. This energy wouldbe diminished accordingly and thus also the possible risks ofintlammability.

For this dual purpose it would also be possible to provide the end ofthe gun with an electrode having a thin edge 23, FIGURE 6, made of highresistivity material for example.

The adjustment of the delivery is effected in this third embodimentexactly as in the embodiment of FIGURES 4 and 5.

Whilst particular embodiments have been described, it will be understoodthat various modifications may be made without departing from the scopeof this invention.

I claim:

l. A spray gun for an electrostatic spray coating process comprising agun body having a hand grip, a hollow sprayer head attached to andinsulated from said body, means for applying a high direct voltage tosaid head, conduit means for delivering sprayable fluid into said head,a plurality of spray discharge orices in said head each having atransverse dimension not greater than about one half a millimeterwhereby said uid will issue from said orices as a spray of discrete,electrically charged particles, a scraper member mounted for rotationwithin said head and engaging the inner surface thereof in the oriticedarea, means for driving the scraper in rotation, a finger operabletrigger control on said grip and means operated by said iinger operabletrigger control for controlling the rotation of said scraper member.

2. A spray gun for an electrostatic spray coating process comprising agun body having grip means for holding said gun, a hollow spraying headattached to and insulated from said body, means for applying a highdirect voltage to said head, conduit means for delivering iiuid to besprayed into the hollow spraying head, a plurality of spray dischargeorices in said head each having a transverse dimension such that saidtuid will issue from said oriiices as a spray of discrete, electricallycharged particles, a scraper member mounted for rotation within saidhead and engaging the inner surface thereof within the region of saidorices, an electric motor mounted on said gun body adjacent said gripand having an insulated motor shaft connected with said scraper memberfor driving said member in rotation, a finger operable trigger controlon said grip and switch means operated by said iinger operable triggercontrol for controlling the energization of said motor.

3. A spray gun as claimed in claim l, wherein said means for driving thescraper member comprises a rotor member rotatably mounted in said bodyin the path of said iluid for rotation thereby and connected to saidscraper member to rotate said member.

4. A spray gun as claimed in claim 1, wherein said means for driving'the scraper member comprises a bladed rotor made of insulating materialand rotatably mounted in said body in the path of said liuid deliveredto the head for rotation by said tiuid, and said scraper member isconnected to a front end of said insulating rotor member.

5. A spray gun as claimed in claim 1, comprising means on said sprayhead providing an electrode having a thin discharge edge.

6. A spray gun as claimed in claim l, including a sleeve slidable over asurface of the spraying head so as to uncover a variable number of saidorifices, and means connecting the sleeve for displacement by saidfinger operable trigger control.

7. A spray gun according to claim l, wherein the internal surface of thespraying head in the zone of said orifices is shaped as a body ofrevolution, the atomizing orilices having their axes directed radiallyof the spraying head and being arranged in circular rows situated inplanes perpendicular tothe longitudinal axis of the spraying head.

8. A spray gun according to claim 3, wherein a return duct for unusedspraying material communicates with the spraying head in order toevacuate the excess material.

9. A spray gun according to claim 8, wherein said ymeans operated bysaid iinger operable trigger control second valves such that as one ofsaid valves opens the other valve closes and vice versa in order toadjust the delivery of said iiuid from said gun.

10. A spray gun for an electrostatic spray coating process'comprising agun body having grip means for holding said gun, a hollow spraying headattached to and insulated from said body, means for applying a highdirect voltage to said head, conduit means for delivering iiuid to besprayed into the hollow spraying head, a plurality of spray dischargeorices in said head dimensioned so that said fluid will issue from saidorifices as a spray of discrete, electrically charged particles, ascraper member mounted for rotation within said head and engaging theinner surface thereof within the region of said oria'ices, means on saidgun for driving the scraper member in rotation, a nger operable triggercontrol on said grip means operated by said finger operable triggercontrol for controlling the rotation of said scraper member, and a hightension electrode disposed in the immediate vicinity of said sprayinghead to decrease dispersion of the electric field.

11. A spray gun for an electrostatic spray coating process comprising agun body having grip means for holding said gun, a hollow spraying headattached to and insulated from said body, means for applying a highdirect voltage to said head, conduit means for delivering uid to besprayed into the hollow spraying head, a plurality of spray dischargeorifices formed through a generally cylinmoving said member to vary thenumber of said orifices drical coaxial wall of said head and dimensionedso that that are uncovered for the discharge of said uid.

said uid will issue from said orifices as a s ray of discrete,electrically charged particles, a scraper iember en- References cned mthe me of this patent gaging the inner surface of the head within theregion 5 UNITED STATES PATENTS of the orifices and means for driving thescraper mem- 636,273 Mine,- Nov' 7, 1899 ber in rotation, alongitudinally movable member fitted 1,454,280 Hem-ikson May g, 1923around said cylindrical wall of the head, a nger oper- 1,493,359 MaueryMay 6', 1924 able trigger control on said grip and means operated by1,608,030 Miller Nov 23, 1926 said iinger operable trigger control forlongitudinally 10 2,558,376 Opp June 26, 1951

1. A SPRAY GUN FOR AN ELECTROSTATIC SPRAY COATING PROCESS COMPRISING A GUN BODY HAVING A HAND GRIP, A HOLLOW SPRAYER HEAD ATTACHED TO AND INSULATED FROM SAID BODY, MEANS FOR APPLYING A HIGH DIRECT VOLTAGE TO SAID HEAD, CONDUIT MEANS FOR DELIVERING SPRAYABLE FLUID INTO SAID HEAD, A PLURALITY OF SPRAY DISCHARGE ORIFICES IN SAID HEAD EACH HAVING A TRANSVERSE DIMENSION NOT GREATER THAN ABOUT ONE HALF A MILLIMETER WHEREBY SAID FLUID WILL ISSUE FROM SAID ORIFICES AS A SPRAY OF DISCRETE, ELECTRICALLY CHARGED PARTICLES, A SCRAPER MEMBER MOUNTED FOR ROTATION WITHIN SAID HEAD AND ENGAGING THE INNER SURFACE THEREOF IN THE ORIFICED AREA, MEANS FOR DRIVING THE SCRAPER IN ROTATION, A FINGER OPERABLE TRIGGER CONTROL ON SAID GRIP AND MEANS OPERATED BY SAID FINGER OPERABLE TRIGGER CONTROL FOR CONTROLLING THE ROTATION OF SAID SCRAPER MEMBER. 